Mineral processing often requires the addition of water. This may result in an overly dilute slurry containing the mineral so that it is necessary to concentrate the finely granulated minerals of the suspension for further processing. Depending on the required final concentration of the mineral, different methods are used for the dewatering process. Besides methods like centrifugation, filtration or evaporation it is known that the dewatering of slurries can be achieved by electrophoresis or electroosmosis leading to the formation of a solid layer or cake.
U.S. Pat. No. 1,133,967 discloses an apparatus for an electroosmotic process having a suspension container and suspension agitating means, which comprise an anode and a cathode locked between the anode and the agitating means, where the cathode is provided with openings of much greater length than width. The anode according to this invention is cylindrical.
U.S. Pat. No. 3,972,799 describes an apparatus for removing solids from drilling mud. The apparatus comprises a horizontal container with a plurality of spaced-apart rotating plate-like discs as anodes arranged between pluralities of spaced-apart interconnected panels as cathodes with a peripheral portion of each disc immersed in the drilling mud, where the discs are rotated by a motor. Solids in suspension are attracted by and deposited as a layer or film on opposing surfaces of the respective discs and stationary scraper blade elements arranged adjacent to the discs remove the deposited solids.
To achieve the exposure of a solid layer or cake from a suspension, rotating anodic discs are proposed by U.S. Pat. No. 4,107,026 that discloses a system and a method for dewatering of a suspension of solids in an electric field controllably maintained between a pair of opposing self-contained electrode structures, to cause the solids to migrate relatively to the carrier liquid to form a layer or cake on the respective self-contained electrode structure, while allowing carrier liquid to be withdrawn under vacuum in the opposite direction through the liquid-pervious wall of a hollow self-contained counter electrode structure, combined with means for controlling the rate of filtrate liquid withdrawal consistent and compatible with the relative speed of migration of the solids in the carrier liquid and wherein said layer or cake material may be detached from said electrode structure, for instance during exposure from the suspension.
In order to increase the efficiency of electrophoretic separation, U.S. Pat. No. 5,171,409 (the equivalent of EP 0 253 749) proposes a process of continuously separating electrically charged, solid pulverous materials in the form of a suspension in an electrophoresis and electroosmosis cell, wherein a fraction of the catholyte is drained off, a portion thereof is treated with an acid, preferably gaseous, agent, the treated portion is re-introduced into the cathode compartment, whereas the other part of the drained-off fraction is eliminated. As the method and device disclosed in this document are very complicated to handle, there is a need for a device that is easy to handle in combination with a high rate of yield.
Although the processes of dewatering suspensions by electrophoresis or electroosmosis are known in the state of the art, both methods are associated with a dissatisfactory degree of mineral cake or solid recovery, especially in the case of calcium carbonate recovery in the form of a sticky mineral cake or solid.